1. Field of the Invention
This invention relates to tire curing bladders and is more particularly concerned with an improved tire curing bladder and with a method for curing tires utilizing said bladder.
2. Description of the Prior Art
It is well-known in the art to shape and cure tire carcasses in a mold using a bladder which contains the curing heat medium and pressure within the carcass to hold the exterior of the latter in contact with the mold during the curing process.
Gostlin U.S. Pat. No 1,378,172 shows an early and primitive bladder curing process in which the exterior of carcass was not confined within a mold. In this method the carcass and the inner bladder (which resembles a conventional inner tube) are placed on a sectional base ring having annular shoulders to hold the bead portions of the carcass in place and having a central annular groove adapted to receive the inner edge of the bladder accurately centered in place. The bladder is inflated to round out the carcass and maintain it under proper tension while being cured. This method lacks the precision and reproducibility of the configurations now demanded of tires to be employed under present conditions as well as requiring an economically unacceptable amount of time and labor to cure the tire carcass.
Semler U.S. Pat. No 1,910,128 describes the use of an air bladder or inner tube which has incorporated therein a heating element to apply heat to the inside of a tire carcass while the latter, encased in a mold, is being cured in a steam kettle.
Frolich et al. U.S. Pat. No. 2,305,412 describes the use of a fabric reinforced air bag resembling an inner tube which is inflated within a tire carcass during the curing process.
Saint Paul U.S. Pat. No. 3,144,374 teaches the use of a cylindrical membrane reinforced with spring steel wires and adapted to be stretched between the flanges of the drum of a tire building machine. The membrane can be deformed to a toroidal shape for constructing uncured tire carcasses. The membrane has limited extensibility in the axial direction of the cylinder due to the limited extensibility of the metal wire reinforcement. In one embodiment the reinforcement comprises a plurality of undulating wires i.e. wires having ,a sine wave configuration. The membrane is not designed for use in a curing process.
Read U.S. Pat. No. 3,547,734 describes a tire building (as opposed to tire curing) air bag fabricated from multiple layers of rubber which have sandwiched therein a reinforcing layer of cords forming a lattice-work pattern with cords aligned in one direction overlapping cords aligned in a different direction, the angle at which the layers of cord cross each other being as much as 45.degree..
Shichman et al U.S. Pat. No. 3,963,394 teaches an expandable bladder for shaping radial ply uncured tire carcasses which has a relatively thick center section and a multiplicity of thinner convolutions. This design provides controlled amounts of extensibility axially. Reinforcing material which can be aramid or steel cords is provided through the center section and end sections of the bladder.
Nicholls et al U.S. Pat. No. 3,979,249 describes an inflatable air bag for tire building machines which has inextensible reinforcing elements, comprising steel, glass fiber and like cords, in part of the width thereof to limit the expansion of the bag in the reinforced areas thereby controlling the shape which the bag assumes upon inflation.
Schmidt U.S. Pat. No. 3,990,930 shows a bladder for use with a tire building drum. The bladder is prepared by first forming a partially cured membrane reinforced with parallel cords running axially. The central portion of the membrane is expanded and has a circumferentially extending belt, optionally reinforced with lattice type material.
MacMillan U.S. Pat. No. 4,030,863 is concerned with providing a separate venting retainer for a cylindrical tire curing bladder. The retainer comprises a net-like cylinder which surrounds the exterior of the bladder and permits escape of air trapped between the inner surface of the tire carcass and the exterior surface of the expanded bladder during the curing operation.
Burley U.S. Pat. No. 4,249,979 describes a fabric reinforced inflatable bladder provided with a ply-folding wedge on its surface and adapted to fold the edges of unvulcanized rubberized ply material around bead wire bundles and the like in the process of building a tire.
We have now found that a tire curing membrane having significantly improved construction and properties can be obtained by providing a membrane with a particular type and configuration of reinforcement not hitherto taught or suggested by any of the prior art discussed above.